This invention relates to electrically conducting and semiconducting materials (including resistors) and is particularly related to electrically conductive patterns on substrates and to methods of forming such patterns.
Electrically conductive patterns are useful in many applications including electrical interconnects, circuit boards, interconnects for very large scale integrated circuits, resistive heating elements, conductors in composite structural materials, fine line conductors for semiconductors, and resistors.
In general, the fabrication of conductive patterns, particularly those requiring fine-line geometries is limited to technologies using photoresist to lift off uniformly deposited metal, or reactive etching of uniformly deposited metal films, or printing techniques using carbon-based inks. These techniques are limited in the types of substrates which are suitable, requiring smooth surfaces such as obtained with polished semiconductors or with some formed plastics and composite substrates. These prior art techniques also suffer from an inability to treat large areas (several square feet) at a time. Additionally, the electrical resistivity values that are achieved are limited, generally approaching the resistivity of the metal being used to form the pattern.
A method of coating a substrate with electrically conductive nickel sulfide is described in U.S. patent application Ser. No. 935,888 filed Nov. 28, 1986 to Leslie F. Warren, Jr. (one of the inventors of the present invention). According to the prior application, a substrate is coated with a solution of a nickel salt and a sulfur donor. The entire coated surface is then heated to provide a uniform coating of nickel sulfide on the substrate. A conducting pattern capable of fine-line geometries is not produced according to the prior application.